BOOKS / Variation on an Enigma: Germany's failure to build the Bomb was a key factor in the Second World War. A new book by Thomas Powers looks at the controversial role of physicist Werner Heisenberg

FEW encounters are as hard to make sense of as the meeting which took place in Copenhagen, in 1941, when Werner Heisenberg, the discoverer of the 'uncertainty' principle, travelled from Berlin on the pretext of a lecture to visit his friend and mentor, the Danish physicist Niels Bohr. What was said that evening remains a matter of passionate dispute more than 50 years on; in later reminiscences the two men failed even to agree whether the conversation took place in Bohr's study or while they were out walking. But there are some who believe that if their talk had turned out differently, so might the Second World War.

Heisenberg was one of the few distinguished German scientists who, rather than accepting the chance to emigrate to the US (which he visited as late as 1939), elected to stay and work for Hitler. How concertedly he helped the Nazi war effort is the subject of Thomas Powers's brilliantly researched and compellingly narrated Heisenberg's War, which argues that Germany's failure to develop the atomic bomb was due not to lack of resources or know-how, but to Heisenberg's procrastination.

About his war record in general Heisenberg has left behind no such unambiguously self-exonerating claim. But he was clear that his visit to Copenhagen in 1941 was made in the 'vague hope' of avoiding nuclear catastrophe. According to his wife Elizabeth, he went there 'to signal to Bohr that Germany neither would nor could build a bomb . . . He hoped that the Americans, if Bohr could tell them this, would perhaps abandon their own incredibly expensive development.'

On that evening in 1941, though, Heisenberg - anxious, inept, afraid of being overheard by SS spies - failed to express himself clearly. And Bohr, annoyed by his former protege's defence of the Nazi invasion of Poland and Russia, then shocked to hear uranium fission being linked with the construction of weapons, was in no mood to decipher cryptic messages. When Heisenberg went on to suggest that scientists worldwide might 'agree among themselves that one should not even attempt work on atomic bombs', Bohr mistrusted his motives. Perhaps Heisenberg wanted Bohr to get the Americans to back off because German research was going badly. Perhaps he feared his beloved Fatherland would become the target of the world's first atomic bomb. Perhaps he was lying, or being used by the Nazi government. Perhaps he was seeking absolution.

The two men parted, Bohr angry, Heisenberg in despair - but not before Heisenberg had drawn a simple sketch to illustrate the work being done in Germany. When Bohr produced this primitive drawing, which looked like a box with sticks protruding from the top, to American scientists in Los Alamos two years later, they took it to be a sketch not of a bomb but of a reactor, and decided they no longer had anything to fear from German atomic research. Bohr, undeterred by his own navety about bomb design, encouraged Robert Oppenheimer to press on with the American nuclear programme none the less, and gave it a new direction and moral centre. Hiroshima followed within 20 months.

'The word 'guilt' does not really apply,' Heisenberg told a fellow German scientist on the morning after Hiroshima, 'even though all of us were links in the causal chain that led to this great tragedy.' But others have not been so ready to excuse him. Heisenberg chose to stay in Germany rather than leave, and his presence at the head of his country's atomic bomb programme spurred the Allies on with theirs - to this extent he was culpable.

But how actively did he work for Hitler from 1939-45? That is the question posed by Thomas Powers, in a book as morally earnest in its way as, say, Christopher Ricks's study of T S Eliot's anti-Semitism, and with the same intention - to dissociate its hero from the evils of Nazism. Heisenberg is one of several creative geniuses this century who brushed too close to Fascism, and this book belongs to the school of posthumous exoneration, defending its hero by unearthing 'what he and his friends said to each other in the small hours of the night, as recorded in memoirs, private letters, diaries, remembered conversations and the files of intelligence services'. The difference between this and other exculpatory biographies is that it examines not just what its subject said, thought and wrote about Nazi Germany, but what he made - or failed to make - on its behalf.

Immediately before the war, Heisenberg's position seemed clear enough. Not yet 40 but already a Nobel prizewinner, handsome and with swept-back blond hair, he was in many ways a Sonnenkind, part of a world in which tearful disagreements about quantum theory co-existed with walking tours and bathing parties and Schubert. He believed science was about 'thinking beyond the point where thinking begins to hurt', but he was no frizz-haired boffin too absorbed in the algebra on the blackboard to read the political writing on the wall. As a friend and defender of Jewish scientists like Einstein and Bohr, he had been vilified as a 'white Jew' and passed over for at least one job that should have been his. He disliked Hitler, was not a member of the Party, and had it not been for a chance family connection with Himmler might have been driven out of the profession. But he survived and fought on, believing he could help create 'islands of decency', steer research in more rational channels, and protect the name of German physics.

Once war came, and Heisenberg in effect headed the Uranverein, the 'uranium club' of physicists carrying out nuclear research, his position looks more dubious, and it's a strength of Powers's book that he does not ignore evidence which undermines his central thesis. At worst Heisenberg made his peace with Hitler, and when visiting abroad defended German military actions. At best he was self-deluding about the pervasiveness of Nazi evil: if you stir the water in a muddy glass, he told a friend in 1942, 'the scum rises to the surface; all the water looks muddy. But give it a chance to rest for a while, and the mud will sink to the bottom, the water will be clear again.' There can be few more craven analogies. Anyone doubting that it was intended as a justification for political quietism need look only at an essay of the same year (quoted by Heisenberg's biographer David Cassidy), in which Heisenberg presents science as a transcendent exercise floating above the blood and mess of history which requires individuals to 'fulfil the duties and tasks that life presents to us without asking much about the why or the wherefore . . . And then we should wait for what happens.' Heisenberg liked to say he was a German, not a Nazi, but from 1939-45 it was a distinction scarcely worth making.

Powers, though, gathers crucial evidence that Heisenberg did - in his own quiet, self- preserving way - actively stall German nuclear research. First he tried to keep the authorities in the dark about the feasibility of manufacturing an atomic bomb: a message smuggled to America in 1941 from his colleague Fritz Houtermans (at a time when Germany was winning the war and pre-emptive repentance in the face of defeat could not have been a factor) said that 'Heisenberg tries to delay the work as much as possible'. Then, in 1942, when Albert Speer was appointed to gee up atomic research, Heisenberg told him that though a bomb was theoretically possible, it could probably not be built in time for use in the war even if billions were invested.

He seems honestly to have believed that there were formidable technical difficulties to overcome, and Powers surely overstates his case when he implies that Heisenberg's use of abstract scientific language was a ruse to bore off eager government officials. Wasn't that, isn't that, just the way scientists talk? And, by the same token, when he cupped his hands to show Nazi officials that the size of a bomb needed to destroy London would be 'no bigger than a pineapple', wasn't he, through such a vivid image, spurring them on? But there can be little doubt that Heisenberg steered a careful course between discouraging all-out efforts to make a nuclear bomb and at the same time convincing the authorities that his work was kriegsentscheidend (decisive for the war effort).

After 1942 Powers changes tack, from science to spying, and to what is almost another book in its own right: a study, blackly comic at times, of American and British efforts to capture or neutralise Heisenberg's brain. The first would-be kidnapper was a beefy colonel fresh out of jungle war in Burma, and the scheme involved an abduction in Germany, a forced march into Switzerland, a secret rendezvous with an American plane and a parachute drop to a waiting submarine in the Mediterranean. Not surprisingly, the plan was abandoned.

But in December 1944, when it was almost too late to matter, American intelligence had a second shot, through Moe Berg, an ex-baseball player fluent in several languages and known as the brainiest catcher ever to play for the Chicago White Sox. Berg walked into a lecture Heisenberg was giving on S-matrix theory in Zurich. 'Discussing math while Rome burns - if they knew what I'm thinking,' Berg scribbled down. Heisenberg, pacing in front of the blackboard, reminded him of the Irish poet Oliver St John Gogarty. Should he kill him? He had a gun in his pocket, and was ready to use it. But he let the moment pass.

Three days after Hitler's suicide, Heisenberg and his brain were finally apprehended. Powers marvellously evokes their sojourn, along with 10 other German scientists, at Farm Hall, near Cambridge, and he is able to draw on documents released by the British government only last year. Secret microphones picked up the group's unguarded and unattractive reactions to Hiroshima on the evening of 6 August, 1945. Heisenberg at first refused to believe it was a uranium bomb; Otto Hahn taunted him as a 'second-rater' for having been beaten by the Americans; Heisenberg's colleague Weizsacker suggested 'the reason we didn't do it was because all the physicists didn't want to do it, on principle'; Karl Wirtz said: 'I think it characteristic that the Germans made the discovery and didn't use it, whereas the Americans have used it.'

These last two remarks incensed post-war commentators: here was moral self-congratulation from Hitler's stooges. But Heisenberg's voice, Powers points out, was 'mostly silent', not self-exculpatory. And Samuel Goudsmit, the fiercest of those to argue that Heisenberg had failed from ignorance, not scruple, had his own hidden agenda. (Heisenberg had failed to intercede on behalf of Goudsmit's parents, who died in Auschwitz.) Besides, if Heisenberg really was so far behind in grasping bomb design, how was he able, within two weeks of Hiroshima, to explain to colleagues how the Allies had constructed their bomb?

Such is Thomas Powers's case, and for those who may have lost their way in the welter of sub-plots and bit-parts, he reiterates it, polemically, in a final chapter. It isn't, in essence, very different from the case Robert Jungk made 37 years ago in his book Brighter than a Thousand Suns, which described Heisenberg's 'strategy of prevention'. But Powers has spoken to many more of the original participants and consulted a vast array of sources. He mounts a formidable defence.

In the end, even he can't deny that the question of Heisenberg's wartime motives will remain forever unanswered. Frustrated, he berates Heisenberg's shade ('you shirked your final duty - to accept responsibility for what you did and tell us about it'), and in the middle of pressing his case suddenly backtracks and admits 'an element of irreducible uncertainty'. In a footnote to this phrase, Powers asks: 'Forgive me.' But neither the word-play, nor the posture, require an apology: it is only too apt that the man whose principle was uncertainty should remain a perpetual enigma.

'Heisenberg's War: The Secret History of the German Bomb' by Thomas Powers, Cape pounds 20